The Open System Interconnection (OSI) reference model is useful in explaining various communications and routing operations. The OSI reference model includes 7 layers with the application layer being the top most layer and the Physical Layer being the lowest layer. The physical layer is the layer which deals with actual physical connections and attributes of the physical connections in the system. Above the physical layer is a Data Link layer, sometimes referred to as the link layer. The link layer (Layer 2 in the OSI model) is sometimes described as a technology specific transfer layer. Above the link layer is the network layer (OSI Layer 3) where network routing and relaying is supported. The network layer is sometimes referred to as the packet layer. It is at the network layer that routing of messages/packets through the network is performed, e.g., on one or more paths. Different addressing may be used for directing messages and signals at the different levels. For example, a network address such as an IP address, maybe used for routing messages/packets at the network layer level. MAC addresses maybe use for controlling routing of messages at the data link layer level. At the lowest level of the OSI model, the physical level, one or more physical identifiers have a relationship to an actual physical attribute or characteristic of a source or destination device. An understanding of the different communication layers and different addressing techniques used for each of the layers will facilitate an understanding of the present invention.
Communications systems frequently include a plurality of network nodes which are coupled to access nodes through which end nodes, e.g., mobile devices, are coupled to the network. Network nodes may be arranged in a hierarchy. End nodes typically communicate with access nodes directly through connections that have been established with said access nodes. Such systems usually rely on the existence of a bidirectional communications link between an access node and end not to support two way communications between an end node and an access node. Note that in such systems the end node normally does not know the network layer address of a target destination access node but may be cognizant of information that it can receive over broadcast channels which typically can include physical layer identifier that are normally not used in such systems for message routing. This approach results in handoff delays and packet loss when the end node is only able to maintain one single bidirectional communications link at the time.
It should then be appreciated that there is a need for methods and apparatus that allows an end node that has no current uplink communications link to a target access node to communicate with said target access node via another access node with which the end node has a current uplink communications link even when said end node does not know the network address of the target access node.
In some systems end nodes are capable of maintaining multiple bidirectional communications links with different access nodes at the same time. However, such systems typically require the end nodes to send messages intended for a specific access node, with which an end node has a connection, over the link that is directly connected to that specific access node. This approach, in some cases, is inefficient since links, especially when they are wireless links, tend to fluctuate in terms of quality (e.g., delay and loss characteristics). As a result the link to the target destination access node may not be the best link available to the end node at the time a message to said target destination access node needs to be sent. Typically this limitation is overcome by resorting to network layer communications that can be routed via multiple hops due to the use of network layer addresses (e.g., IP addresses). This approach of using network layer addresses is also inefficient especially when the messaging has to do with link layer specific functions, since network layer messages tend to be much larger than link layer messages in some systems. Such inefficient signaling is not well suited for communications over resource restricted air links.
It should then be appreciated that there is also a need for a method that allows an end node to send messages over any of its available wireless communications links independently of the access node the message is intended. It would be desirable is such messages could be sent, at least in some embodiments, without having to resort to inefficient network layer communications, e.g., communications involving the use of network layer addresses, such as IP layer addresses, for routing information to the destination access node.